The making of lenses and lens arrays is an extremely important part of modern technology, particularly in optics and photonics. Lenses at the macro-scale (i.e., a few centimeters in diameter or larger) can be made using a variety of methods, including various machining methods (e.g., diamond turning, etc.), molding, embossing, etc., to obtain adequately high levels of precision for most applications. The fabrication of lenses and lens arrays at the micro-scale is a more recent development and has become a very important part of modern semiconductor manufacturing. These micro-lenses and micro-lens arrays are typically made using specialized semiconductor processes to allow the implementation of lens profiles with performance far inferior to that of similar types of lenses made at the macro-scale. These methods include: photolithography of a resist pattern followed by a re-flow of the resist and a subsequent Reactive Ion Etching (RIE) of the underlying substrate to form a curved and smooth lens shape; gray-scale lithography followed by a RIE; micromachining fabrication of a tool mold having the lens pattern on it followed by hot embossing or molding of a material into the lens shape; the direct micromachining of a substrate surface using a focused ion beam (FIB); etc.
While these methods have allowed the implementation of lenses and lens arrays at the small dimensional size, including the micro-scale, they have several shortcomings. First, these methods involve fabrication processes that are extremely difficult to control or to obtain reproducible results from batch to batch. As a result, the yield of these methods can be quite low with the resultant consequence of higher cost components. Second, most of these processes result in some significant distortions of the lens shapes with negative consequences for the performance of the lenses or lens arrays. Third, the surface smoothness of RIE etched or FIB machined surfaces are typically very rough (e.g., more than a few nanometers) which degrade the performance of the lens elements due to photon scattering as well as other effects. Fourth, the use of a FIB tool to make lenses is an extremely slow process, is performed on a very expensive tool, and is, therefore, an extremely expensive method to make lenses and lens arrays. Fifth, the use of molding and embossing allows the high cost of the tool mold to be amortized over many parts, so as to obtain a relatively low cost method for making lenses and lens arrays; however, molding and embossing is an elevated temperature process, and the materials used in these processes tend to have large thermal expansion coefficients, thereby resulting in lens shapes that distort as the lens material cools back to room temperature. Sixth, none of the methods discovered to date allow the fabrication of extremely small-dimensioned lenses and lens arrays. The existing methods are limited to lenses having a diameter of at least tens to hundreds of microns, or more. Seventh, as the lower limit of the dimensions that lenses and lens arrays can be fabricated using existing methods are approached, the distortions on the shape of the lenses, surface roughness of the lens, as well as other quality aspects of the lens increasingly and quickly degrade. Consequently, there is an enormous opportunity for a new technique, whereby lenses and lens arrays can be fabricated that have excellent optical properties.